Constant velocity joints and similar rotating couplings operate to transmit torque between two rotational members. The constant velocity joint typically includes an inner joint member for engagement with one rotational member, an outer joint member for engagement with the other rotational member, and a boot cover assembly or a grease cover to enclose and protect the rotating assembly positioned within the outer member during operation. Since the boot cover assembly is partially flexible, the boot cover assembly is able to seal around one of the rotating members while permitting articulation and relative axial movement between the two rotating members. The boot cover assembly provides a barrier to retain the grease in the internal cavity of the joint so as to reduce friction and extend the life of the joint. The boot cover assembly helps to seal out dirt, water and other contaminants to protect the functionality of the joint.
Constant velocity joints require constant lubrication (grease) to remain in operation in the environment in which they are utilized. Typically, such joints use a sealed system to contain the grease, the main component of which is the boot cover assembly that includes a boot and associated mounting can. Boots come in a variety of types. Some examples include convoluted, internal rolling diaphragm (IRD) and external rolling diaphragm (ERD). Particularly relating to IRD and ERD boots, the current industry standard is to have the diaphragm boot crimped onto the mounting can, and then to have the mounting can fit onto the joint. The mounting can and boot may be vulcanized together or crimped together at the top only, which allows grease that is under pressure from centrifugal forces during the joint rotation to be pushed between the sides of the boot and the mounting can (blow-out).
However, an important characteristic of the constant velocity joint is the ability of the joint to allow relative axial movement between two shafts while maintaining a seal to the outside environment. Typically, constant velocity joints include a seal groove that extends circumferentially about the outer surface of the outer member. This groove is generally machined or cut into the outer joint member, causing additional labor, cost and time. The groove provides a channel for receiving and positioning an o-ring type seal at a connection point between the boot assembly, boot-can and the outer member of the constant velocity joint. The seal is used to help prevent the blow-out phenomenon associated with the build-up of pressure.
Additionally, the centrifugal forces and friction associated with the internal components of the constant velocity joint assembly result in expansion or ballooning of the flexible boot cover as a result of the pressure created from heat and high speed operation. The deformation of the flexible boot cover may be affected by lubricant load, a pumping action of the lubricant due to constant velocity joint articulation, temperature, speed, release of gas volatiles from the grease, and the shape of the flexible boot. The constant expansion and contraction of the flexible member results in fatigue, wear and eventual failure of the flexible boot and ultimately the constant velocity joint. Typically, a vent is provided to relieve any pressure and minimize or eliminate the expansion of the flexible boot. However, this vent also allows dirt, water and other debris to enter the constant velocity joint. Specifically, venting the constant velocity joint can lead to lubricant leakage or loss, as well as the infiltration of contaminants into the joint, reducing its overall life.
What is needed, therefore, is a constant velocity joint and boot cover assembly that eliminates the need for a separate seal disposed about the outer surface of the outer member. Additionally, there is a need for a constant velocity joint and boot cover assembly that is configured to eliminate the need for a flexible boot vent.